A conventional frequency modulated continuous wave (FMCW) radar altimeter system is limited to 200 MHz of operating bandwidth that corresponds to around 3 feet of range resolution. Such an FMCW radar operates by transmitting a chirp signal (frequency sweep) and determining a distance to a target based on the time between transmission of the chirp signal and a reception of a reflection of the chirp signal. The chirp signal is repeated to continually measure distance. The chirp signal can be a linearly increasing ramp, that is repeated, or a linearly increasing ramp followed by a linearly decreasing ramp that is repeated. Such FMCW radars can be used as altimeters in an aircraft or airborne vehicle.
The leading edge detection scheme is known to potentially bias the altitude to a lower value (i.e., a shorter distance) than is correct. For example in the case of a large target, the leading edge detection scheme may track the leading edge range side lobe rather than the actual peak of return.